It is often necessary to verify in real time the mechanical integrity of materials having large areas to assure satisfactory quality of an article or workpiece. It is especially important to assure integrity and quality in aircraft componentry where the failure of components may have life threatening consequences. In other applications, it is important to inspect or monitor the workpiece or member in real time even while the workpiece or member is subjected to stress.
Many non-destructive inspection techniques have been developed in the past. Eddy current inspection techniques, in particular, have been employed for a number of years for the inspection of materials having conductive surfaces, however, known eddy current probes have proved ineffective in differentiating the presence of multiple defects and sensing small surface defects below 0.010. One form of eddy current probe known in the art employs a coil which is scanned over the surface to be inspected. A defect in the surface, of sufficient size, causes a change in the electrical impedance of the coil. The probe produces an output signal indicative of defects proximate to the eddy current probe. An extremely small area coil is needed to permit detection of small defects. The prior art eddy current probes, even of small area, have not been effective in reliably detecting defects of less than 0.010 inches in length. Additionally, the use of eddy current coil probes requires the time consuming and inexacting process of X-Y scanning to complete inspection of a large area surface.
One eddy current defect sensor is disclosed a co-pending U.S. patent application of the same inventor and assignee as the present disclosure which is capable of detecting defects smaller than 0.010 inches. In this disclosure eddy currents are induced in a conductive workpiece by one or more wires disposed along a path parallel to a first axis, and defects are sensed with one or more wires disposed along a path perpendicular to and intersecting the first axis.
Another apparatus and method for eddy current detection of subsurface discontinuities in a conductive body is disclosed in U.S. Pat. No. 4,271,393 to Hansen, et al.